This disclosure relates to fabrication of thin film photovoltaic cells.
Thin film solar cells, also known as thin film photovoltaic cells, are used to convert light energy directly into electrical energy. The manufacture of thin film solar cells includes the steps of sequentially depositing one or more thin film layers onto a substrate. A thin film solar cell usually includes a bottom layer, a back electrode layer, an absorber layer, a buffer layer, and front contact layer. Many thin film solar cells use a “CIGS-based” absorber in the absorber layer, where “CIGS” generally refers to Copper-Indium-Gallium-Selenide or Cu(In,Ga)Se2.
CIGS materials are typically prepared in solution by dissolving the constituent compounds such as In2Se3, Cu2S, Ga2(SO4)2, SeO2, CuCl2.2H2O, and InCl3.nH2O in solvents such as hydrazine, ethylene glycol, dismethylsulfoxide, and dimethyformamide. In some circumstances, treatment with heat and acids such as HCl are used to initiate compound dissolution in the solvent. These solutions are then usually mixed, spin-coated onto the substrate or back electrode layer, and crystallized. In some circumstances, the precipitates of such solutions are filtered, washed, and dried for later deposition onto the substrate or back electrode layer. This solution-based process has the advantages of high throughput during CIGS manufacturing.